[R ] Query : problems with the arithmetic operator "^" with function "lme" and "lmList"

-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch 
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of MARTIN

Sent: Wednesday, May 07, 2003 7:02 AM
To: r-help at stat.math.ethz.ch
Subject: [R] [R ] Query : problems with the arithmetic 
operator "^" withfunction "lme" and "lmList"


Dear all,

I've got a problem in including square variables in lme and lmlist 
functions. I've tried to work on Oxboys data of Pinheiro and 
Bates'book, which consist of the heights of 26 boys, each mesured on 
nine different occasions :

Oxboys

Grouped Data: height ~ age | Subject
   Subject     age height Occasion
1         1 -1.0000 140.50        1
2         1 -0.7479 143.40        2
3         1 -0.4630 144.80        3
4         1 -0.1643 147.10        4
5         1 -0.0027 147.70        5
...

A quadratic model in "age" would be fit with lmList
(height~age+age^2,Oxboys).

We obtain:

fm2Oxboys.lis<-lmList(height~age+age^2,Oxboys)
fm2Oxboys.lis

Call:
 Model: height ~ age + age^2 | Subject 
  Data: Oxboys 

Coefficients:
  (Intercept)      age
10    130.2616 3.722915
26    137.9927 5.588783
25    139.2105 4.024081
9     138.1369 6.009057
2     142.8584 5.440176
...
19    164.5761 9.065620
4     165.0724 9.360561

Degrees of freedom: 234 total; 182 residual
Residual standard error: 0.6598878

They are not coefficients associated with the covariate "age^2" ! 
However, the model called is " Height~age+age^2 | Subject " .

I would be grateful if anyone could help me.

Cordially,

Martin Ludovic.